This
report explains the Twiddler's syndrome, a well known human entity, in
a canine model. We also describe a modified technique to
implant internal cardioverter defibrillators (ICD) in dogs to prevent
Twiddler's syndrome. Our original study was to identify the factors
influencing the DFT measurement and a canine model was selected as it
is the best proven electrophysiological model. During the course of
the study, one of the dogs was evaluated for device failure at three
weeks following implantation. While under general anesthesia,
interrogation of the dog's ICD showed that the right ventricular (RV)
pacing threshold was high and ventricular capture was intermittent.
When examined under fluoroscopy, it was noted that the defibrillator
lead was dislodged from the right ventricular apex. A surgical revision
of the device pocket showed that the leads were twisted in an almost
braided fashion - as if "twiddled" into position around the device [Figure1 (arrow)]. We suspect that
this "twiddling" resulted in shortening and pulling of the lead from
the ventricular myocardium causing intermittent capture and device
failure.

Figure 1

Twiddler's syndrome, a not uncommon occurrence in human clinical
cardiology practice, was first described by Bayliss et al. [1] It is
likely to occur when an implanted pulse generator or ICD is rotated in
the subcutaneous pocket resulting in malfunction of the device.
Interestingly, Twiddler's syndrome has also been reported in animals
[2]. Twiddling of the pacemaker leading to twisting of the lead in
animals may be more common than reported as it is usually implanted in
a pocket fashioned in the neck region where the subcutaneous tissue is
loose. In our dog, during the original implantation, the RV lead was
implanted via the left external jugular vein (LEJ) access [Figure1 (arrowhead)] and the lead
was tunneled deep to the subcutaneous tissue via the left ventrolateral
neck over the distal end of the left humerus to a subcutaneous pocket
prepared by digital dissection on the left lateral thorax. The
"twiddling" may be caused by scratching of the cranial chest region
with a hind paw or may be due to local muscular action during normal
activities [2]. A surgical revision was performed in our dog where the
"twiddled" lead was untwisted, extracted and a new defibrillator lead
was implanted and secured in RV apical position. To prevent the
"twiddling", the new lead was tunneled deep to the subcutaneous tissue
over the dog's left shoulder dorsally from the LEJ to a new
subcutaneous device pocket in the lateral chest wall. (Figure 2) This approach essentially
minimized the device movement and hence "twiddling" by the hind paw. We
observed the dog closely for three months post re-implantation; the
sensing and pacing threshold and lead impedance were within normal
limits. Since animal models are being used more frequently to perform
electrophysiological studies, this observation of Twiddler's Syndrome
in the canine may be of interest.

Figure
2

The entire study was done under general anesthesia with special
emphasis on perioperative and postoperative pain management. All
experimental procedures and protocols used in this investigation were
reviewed and approved by the Animal Care and Use Committee of the Wayne
State University. All conformed to the "Guiding Principles in the Care
and Use of Animals" of the American Physiological Society and the Guide
for the Care and Use of Laboratory Animals of the National Institutes
of Health (Revised, 1996).